email blocked from sending

Question

i am getting this message, not sure how to fix, my email address is correct

This message couldn't be delivered because the sending email address was not recognized as a valid sender. The most common reason for this error is that the email address is, or was, suspected of sending spam. Contact the organization's email admin for help and give them this error message.

Answer 1

Hello

Does this happen to only sending to a specific email address, or it doesn't matter who you emailed?

This is from your outlook.com address, right?

Answer 2

The error indicates the account has been blocked as a bad outbound sender because it exceeded spam/sending limits or was suspected of sending spam.

Steps depend on the role:

1. As the mailbox user
   • Check whether the account might be compromised:
     • Look in Sent Items for messages not sent personally.
     • If anything looks suspicious, immediately change the account password and scan devices for malware.
     • Follow the guidance in determine whether your account is compromised.
   • Inform the organization’s email administrator that this specific error is being received and that the account may be blocked for outbound mail.
2. As the email administrator
   • Secure the account:
     • Follow Secure a compromised email account in Exchange Online to remove any malicious rules, delegates, or forwarding.
   • Unblock the user:
     • Go to Microsoft 365 Defender portal → Restricted entities page (https://security.microsoft.com/restrictedusers).
     • Locate the affected user and remove them from the restricted list.
     • After unblocking, sending restrictions are usually removed within about an hour.
   • Review and harden security to prevent recurrence using the recommendations in Top 10 ways to secure your business data.

If the problem persists after the account is secured and unblocked, contact Microsoft Support through the normal support channel with the full NDR text.

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References:

• NDR error code "550 5.1.8 Access denied, bad outbound sender"
• Email non-delivery reports and SMTP errors in Exchange Online
• Fix NDR error "550 5.1.0" in Exchange Online